In Release 12 (Rel-12), the Long Term Evolution (LTE) standard was extended with support for device-to-device (D2D) (specified as “sidelink”) features targeting both commercial and public safety applications. One application enabled by Rel-12 LTE is device discovery, where devices are able to sense the proximity of other devices and associated applications by broadcasting and detecting discovery messages that carry device and application identities. Another application is direct communication based on physical channels terminated directly between devices.
A potential extension for D2D technology is support of vehicle-to-other (V2x) communication, which includes any combination of direct communication between vehicles and other entities, such as pedestrians and infrastructure. Examples of V2x communication include vehicle-to-vehicle (V2V) communication, vehicle-to-pedestrian (V2P) communication, and vehicle-to-infrastructure (V2I) communication, to name but a few.
V2x communication may take advantage of a network (NW) infrastructure when available, but at least basic V2x connectivity should be possible even with a lack of NW coverage. Providing an LTE-based V2x interface may be economically advantageous because of LTE economies of scale. It may also enable tighter integration between communications with the NW infrastructure (V2I) and V2P and V2V communications, as compared to using a dedicated V2x technology.
V2x communication may carry both non-safety and safety information, where each of the applications and services may be associated with specific requirements sets, e.g., in terms of latency, reliability, capacity, etc.
The European Telecommunications Standards Institute (ETSI) has defined two types of messages for road safety: Co-operative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM).
A CAM message is intended to enable vehicles, including emergency vehicles, to notify their presence and other relevant parameters in a broadcast fashion. Such messages target other vehicles, pedestrians, and infrastructure, and are handled by their applications. CAM messages also provide active assistance for safe driving in normal traffic. The availability of a CAM message is indicatively checked for every 100 ms, yielding a detection latency requirement of <=100 ms for most messages. However, the maximum latency requirement for a Pre-crash sensing warning is 50 ms.
A DENM message is event-triggered, such as by braking, and the availability of a DENM message is also checked for every 100 ms. The latency requirement for a DENM message is <=100 ms.
The package size of CAM and DENM messages varies from 100+ to 800+ bytes and the typical size is around 300 bytes. Such messages are supposed to be detectable by all vehicles in proximity.
The Society of the Automotive Engineers (SAE) also defined the Basic Safety Message (BSM) for DSRC with various messages sizes defined. According to the importance and urgency of the messages, the BSMs are further classified into different priorities.
In V2x communications, the end-to-end latencies experienced when using resource allocation algorithms for common applications may not meet the tight requirements of urgent messages. In addition, resource allocation algorithms based on scheduling periods may not allow for instantaneous transmission of urgent messages.